I've been working with Groklaw's heretic on a patents resource page, and in the course of that project, I realized that we never put up the Dear Linux User letter [PDF] as text. So here it is, at long last.

In May 2003, SCO warned about enterprise use of the Linux operating system in violation of its intellectual property rights in UNIX technology. Without exhausting or explaining all potential claims, this letter addresses one specific area in which certain versions of Linux violate SCO's rights in UNIX.

In this letter we are identifying a portion of our copyright protected code that has been incorporated into Linux without our authorization. Also, our copyright management information has been removed from these files.

These facts support our position that the use of the Linux operating system in a commercial setting violates our rights under the United States Copyright Act, including the Digital Millennium Copyright Act. We are notifying you of these facts so you can take steps to discontinue these violations. We believe these violations are serious, and we will take appropriate actions to protect our rights. No one may use our copyrighted code except as authorized by us. The details of our position are set forth below. Once you have reviewed our position, we will be happy to further discuss your options and work with you to remedy this problem.

Certain copyrighted application binary interfaces (“ABI Code”) have been copied verbatim from our copyrighted UNIX code base and contributed to Linux for distribution under the General Public License (“GPL”) without proper authorization and without copyright attribution. While some application programming interfaces (“API Code”) have been made available over the years through POSIX and other open standards, the UNIX ABI Code has only been made available under copyright restrictions. AT&T made these binary interfaces available in order to support application development to UNIX operating systems and to assist UNIX licensees in the development process. The UNIX ABIs were never intended or authorized for unrestricted use or distribution under the GPL in Linux. As the copyright holder, SCO has never granted such permission. Nevertheless, many of the ABIs contained in Linux, and improperly distributed under the GPL, are direct copies of our UNIX copyrighted software code.

Any part of any Linux file that includes the copyrighted binary interface code must be removed. Files in Linux version 2.4.21 and other versions that incorporate the copyrighted binary interfaces include:

The code identified above was also part of a settlement agreement between the University of California at Berkeley and Berkeley Systems Development, Inc. (collectively “BSDI”) and UNIX Systems Laboratories, Inc. regarding alleged violations by BSDI of USL's rights in UNIX technology. The settlement agreement between USL and BSDI addressed conditions upon which BSDI could continue to distribute its version of UNIX, BSD Lite 4.4, or any successor versions, including certain “UNIX Derived Files” which include the ABI Code. A complete listing of the UNIX Derived Files is attached. The ABI Code identified above is part of the UNIX Derived Files and, as such, must carry USL / SCO copyright notices and may not be used in any GPL distribution,

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inasmuch as the affirmative consent of the copyright holder has not been obtained, and will not be obtained, for such a distribution under the GPL.

Use in Linux of any ABI Code or other UNIX Derived Files identified above constitutes a violation of the United States Copyright Act. Distribution of the copyrighted ABI Code, or binary code compiled using the ABI code, with copyright management information deleted or altered, violates the Digital Millennium Copyright Act (“DMCA”) codified by Congress at 17 U.S.C. §1202. DMCA liability extends to those who have reasonable grounds to know that a distribution (or re-distribution as required by the GPL) of the altered code or copyright information will induce, enable, facilitate, or conceal an infringement of any right under the DMCA. In addition, neither SCO nor any predecessor in interest has ever placed an affirmative notice in Linux that the copyrighted code in question could be used or distributed under the GPL. As a result, any distribution of Linux by a software vendor or a re-distribution of Linux by an end user that contains any of the identified UNIX code violates SCO's rights under the DMCA, insofar as the distributor knows of these violations.

As stated above, SCO's review is ongoing and will involve additional disclosures of code misappropriation. Certain UNIX code, methods and concepts, which we also claim are being used improperly in Linux, will be produced in the pending litigation between SCO and IBM under a confidentiality order.